Cut the lobe of foie gras in slices of about 3/4" to 1". Carefully remove large veins. Salt and pepper each side. Marinate the foie gras and truffle slices in Armagnac, for a couple of hours.

Remove the foie gras from the marinade, wipe dry and sprinkle the flour on both sides. Combine the Demi-Glace with the truffles and Armagnac and heat slowly. Meanwhile, sear the foie gras slices in a pan over high heat with a few drops of olive oil, browning both sides, but being sure not to overcook. Remove the foie gras from the pan.

Toast the brioche rounds, or if using bread, fry the rounds in olive oil or butter. Serve the foie gras slice over a brioche or bread round, and top with sauce and truffle slices.